The present invention relates to imide-modified vinylaromatic polymers and copolymers. Vinylaromatic polymers and copolymers, such as polystyrene, SAN and ABS are important classes of thermoplastic polymeric materials. Their impact resistance, tensile and flexural strength, and elongation values make these polymers extremely useful in fields where strength, durability and ease of manufacture are desired. The polystyrene thermoplastic resins are conventionally molded in sheet form and structural form, designed and adaptable as packaging structures, housings, support structures, furniture molded articles, toys, architectural trim, motor housings, television cabinets, and the like. In many applications, such as vehicles, the building trades, electrical appliances and consumer goods, heat resistance of polymeric materials is a highly desirable property. Like most thermoplastic resins, there is a desire to increase the heat resistance of vinylaromatic resins without negatively detracting from other desirable properties of these polymers.
A variety of approaches to improving heat resistance of thermoplastic vinylaromatic resins have been explored. For example, organic and inorganic fire retardants have been effective but are difficult to homogenously disperse in the polymer, which not only can give rise to poor surface appearance, but can also negatively affect heat resistance. Attempts have also been made to take advantage of the high heat resistance of polyimides by interpolymerizing phenylmaleimide with vinylaromatic monomer compositions. While the resulting interpolymers do exhibit improved heat resistance, the phenylmaleimide monomer significantly raises the cost of the polymer product, because it is difficult to prepare and purify. In addition, it is the only arylmaleimide monomer currently commercially available.
Another approach to preparing imide-containing polymers is to post-imidize maleic anhydride-containing polymers. For example, a styrene-maleic anhydride copolymer may be reacted with a primary amine, such as aniline, to yield a styrene-phenylmaleimide copolymer. The difficulties associated with the use of maleic anhydride in polymerization processes make this approach to imide-containing polymers unattractive.